Washington:
Swiss researchers has revealed that a drug commonly
used treat altitude-related symptoms in mountaineers can
also improve their exercise capacity at high altitude.
Dexamathasone prophlyactically is popular among climbers
as 'dex'. "We have known that both tadalafil and dexamethasone
are good for preventing high altitude pulmonary edema
(HAPE) and dex for treating symptoms of acute mountain
sickness (AMS)," said lead authors Dr Manuel Fischler,
of the University Hospital in Zurich, Switzerland, and
Hans-Peter Brunner-La Rocca, of the University Hospital
in Basel, Switzerland. "But we did not know whether they
could also improve exercise capacity at altitude by reducing
pulmonary hypertension, one of the important factors in
altitude-related exercise limitations," they added. During
the study, the researchers recruited 23 mountaineers with
a history of HAPE and administered baseline cardiopulmonary
exercise tests a low elevation (490 meters, or 1607 feet).
Subjects were tested for oxygen uptake kinetics by pedaling
a stationary bike at a constant rate for six minutes,
and then for exercise capacity by pedaling at 50 percent
of their predicted maximum workload for one minute, then
increasing output by 25 percent each additional minute
until exhaustion, usually after 8 to 12 minutes. "At low
altitude, peak exercise performance of subjects was significantly
above age- and gender-adjusted normal values, indicating
superior fitness in these subjects," noted Dr. Fischler.
All participants were randomised to take tadalifil, dexamethasone
or placebo, beginning the day before a cable-car ascent
from Alagna, Italy, at 1,100 meters (3,609 feet), to 3,200
meters (10,499 feet). They then ascended on foot to Capanna
Gnifetti at 3,650 meters (11,975 feet). After an overnight
stay at Capanna Gnifetti, the climbers finally ascended
to Capanna Regina Margherita at 4,559 meters (14,957 feet).
The cardiopulmonary exercise tests were performed 4-5
hours after arrival, and echocardiographic examinations
were performed the next day. "Reduced oxygen content in
the air is the major limiting factor at high altitude.
Reduction in exercise capacity goes in parallel to the
reduction in oxygen up to an altitude of approximately
4000 meters. At higher altitudes, there is an even further
reduction in exercise capacity," said Dr. Fischler. "As
expected, exercise capacity at high altitudes was diminished
among all groups and key indictors of cardiopulmonary
stress were elevated," he added. Both tadalafil and dexamethasone
subjects showed a smaller drop in oxygen saturation over
the placebo group, indicating a better uptake of oxygen,
and a measure of pulmonary artery pressure was significantly
less for both tadalifil and dexamethasone groups over
placebo. "Our study indicates that for HAPE-susceptible
climbers, taking dexamethasone improved exercise capacity,
oxygen uptake kinetics and decreased the anaerobic threshold,"
said Dr. Fischler. "Overall, this means that those climbers
who took dex felt better, were able to do more, and probably
experienced fewer altitude-related discomforts than both
other groups." The study appears in American Journal of
Respiratory and Critical Care Medicine. -August
12, 2009